The present invention relates to a magnetic head supporting device for use with a magnetic disk driving device for recording or reproducing information with respect to a disk-like magnetic recording medium.
Such a magnetic disk driving device for recording or reproducing information with respect to a disk-like magnetic recording medium (which will be hereinafter referred to as a disk) is widely used as an external storage for an information processing apparatus such as computer and work processor.
An example of the information processing apparatus is a so-called still video floppy disk driving device. The disk driving device is installed in a still video floppy camera, and it is designed to record video information on a still video floppy disk in the same manner as with a camera device using a photosensitive film.
This type of disk driving device is disclosed in Japanese Patent Laid-open Publication No. 58-57667, for example. In this prior art disk driving device, a holder for holding a disk cartridge containing a disk is rotatably supported to a mounting substrate having a rotating bed. In loading the disk, the disk cartridge is inserted into the holder, and the holder is rotated to the mounting substrate to load the disk in the disk cartridge onto the rotating bed. A restriction plate for applying a load pressure is mounted to a case cover, and it is opposed to a magnetic head with the disk interposed therebetween when the disk is loaded.
Another disk driving device capable of stabilizing the contact between the disk and a gap of the magnetic head without using the above-mentioned restriction plate is disclosed in Japanese Utililty Model Publication No. 42-17806, for example.
This prior art relates to a device for recording and reproducing a signal as rotating a very thin magnetic disk sheet of 50 .mu. or less thick at a high speed such that the magnetic disk sheet can be maintained under a planar condition by a centrifugal force. A base mounting the sheet thereon is formed with a recess where a magnetic head is adjustably received. The recess is slightly inclined in a direction opposite to a rotative direction of the sheet in accordance with deformation of the sheet passing over the recess. During the rotation of the sheet, the pressure between the magnetic sheet and the base is rendered slightly smaller than the pressure over the magnetic sheet, resulting that the magnetic sheet is sunk into the recess. Accordingly, the contact between the magnetic sheet and a head gap of the magnetic head projecting upwardly from a head mounting surface may be stabilized.
The still video floppy disk driving device (which will be hereinafter referred to as SVF device) in the former prior art is provided with two head gaps so as to record and reproduce a frame image. Accordingly, a difference in opposing condition and load pressure of the disk to the two head gaps causes a difference in recording and reproducing performance of field images, resulting in a deterioration of picture quality of the frame image. Therefore, adjustment of the image by a spacing adjusting screw is greatly important in the structure having the aforementioned restriction plate. However, since the restriction plate is flat, a slight difference in inclination of the restriction plate causes a great change in picture quality. Thus, the adjustment is greatly difficult. Further, since a peripheral speed of the disk at its radially inner position is different from that at its radially outer position, a relative speed between the disk and the restriction plate at the radially inner position is different from that at the radially outer position, causing a change in positional relation of the disk relative to the two head gaps between at the radially inner and outer positions. As a result, a fine difference in image is generated.
In the latter prior art, the disk sheet is flexed as if it were sucked into the recess to face the head gap of the magnetic head under constant condition. Accordingly, it is possible to maintain a constant video quality in recording and reproducing information without the necessity of especially restricting the position of the disk sheet with respect to the head gap.
However, the inventor has found that the SVF device in the latter prior art has a shortcoming such that the disk adheres to a sheet bed to cause incapability of rotation of the disk. Such a phenomenon depends on two factors consisting of a surface roughness of an outer peripheral projection of the sheet bed and a humidity in the air. If the two factors satisfy certain conditions, the above phenomenon will be assumed to occur. When the disk adheres to the sheet bed, the air in the recess appears to be sealed by the disk. Although such adherence of the disk disappears after a given time (about 10 seconds) to permit the rotation of the disk, continuous photographing is interrupted by the adherence of the disk. Especially, in applying the SVF device to data recording, there is a possibility that data writing/reading will be rendered impossible, which means instability of writing/reading.
In connection with adherence of the disk, there is a possibility of dewing on an inside surface of the disk in the recess. This phenomenon will now be described with reference to FIG. 4.
As shown in FIG. 4, a magnetic head support 11 is formed at at least its outer circumference with an annular projection 12 and a recess 13 surrounded by the annular projection 12. The recess 13 has a depth D of about 50 .mu.m from an upper surface 14 of the projection 12. The upper surface 14 is opposed to a lower surface of a disk 15 with a gap L of 1 .mu.m or less defined therebetween. With this arrangement, when an air flow created by rotation of the disk 15 passes through the gap L into the recess 13, the air is suddenly expanded. Namely, adiabatic expansion of the air occurs. As a result, it is considered that pressure and temperature of the air in the recess 13 are reduced to cause dewing W on the inner surfaces of the disk 15 and the projection 12 in the vicinity of a position where the air has entered the recess 13. In this case, the surface roughness of the upper surface 14 of the projection 12 ranges from 0.05 S to 0.1 S.
The occurrence of the dewing W causes wetting of the recording surface of the disk 15 (the lower surface as viewed in FIG. 4) to adversely affect the recording/reproducing performance. Moreover, the gap L between the upper surface 14 of the projection 12 and the lower surface of the disk 15 tends to be closed by the dewing W, causing promotion of the adherence of the disk 15 to the support 11.